As one system for displaying a large-screen image, projection display devices are known that use, as an image forming means, a small-sized spatial light modulation element that forms an optical image in accordance with a video signal, and such an optical image is illuminated to project the optical image in a magnified state using a projection lens. And, projection display devices such as a projector, that use a liquid crystal panel as a spatial light modulation element, have been put into practical use. For such projection display devices, there is a strong need to increase the brightness of projected images, and in order to meet such a need a projection display device that includes a light source device configured with a plurality of lamps is disclosed in Patent Document 1, for example.
FIG. 6 shows a configuration example of such a projection display device. This projection display device includes discharge lamps 31 and 32, ellipsoidal mirrors 33 and 34, UV-IR cut-off filters 35 and 36, plane mirrors 37 and 38, a reflecting prism 39, a condenser lens 40, a first lens array 41, a second lens array 42, a beam-combining lens 43, a field lens 44, a liquid crystal panel 45, and a projection lens 46.
Metal halide lamps, ultra-high pressure mercury lamps, xenon lamps, or the like may be used as the discharge lamps 31 and 32. Light beams emitted from the lamps 31 and 32 are condensed with the respective ellipsoidal mirrors 33 and 34, and the ultraviolet light and infrared light components are removed with the UV-IR cut-off filters 35 and 36 before their optical paths are bent by the plane mirrors 37 and 38. The reflecting prism 39 is disposed in the vicinity of second focal points of the ellipsoidal mirrors 33 and 34. Consequently, the condensed light spots of the lamps 31 and 32 are formed in the vicinity of reflection planes 39a of the reflecting prism 39.
The reflection planes 39a of the reflecting prism 39 are provided with an aluminum film or a dielectric multilayer film vapor-deposited thereon, at which visible light is reflected efficiently. Light reflected at the reflecting prism 39 is divergent light, and is incident on the condenser lens 40. As the condenser lens 40, it is possible to use, for example, an aspherical double-convex lens, which converts the incident light into substantially parallel light.
Bundles of parallel light from the condenser lens 40 are incident on the first lens array 41 including a plurality of lenses, and are split into a large number of minute light beams. The large number of minute light beams converge onto their respective corresponding lenses of the second lens array 42 including a plurality of lenses. Accordingly, a large number of images of the lamps 31 and 32 are formed on the second lens array 42. The second lens array 42 has the same shape as the first lens array 41.
Each of the rectangular lenses of the second lens array 42 magnifies the minute light beams incident on the surface of the corresponding rectangular lens of the first lens array 41, and thereby, the surface of the liquid crystal panel 45 is illuminated. The beam-combining lens 43 is used to superpose the light beams exiting from the rectangular lenses of the second lens array 42 on the liquid crystal panel 45.
By splitting the light beams incident on the first lens array 41 into a large number of minute light beams, and superposing the light beams in a magnified state on the liquid crystal panel 45, it is possible to illuminate the surface of the liquid crystal panel 45 with good uniformity.
The field lens 44 is used to condense the light illuminating the surface of the liquid crystal panel 45 onto the pupil plane of the projection lens 46. The projection lens 46 projects an optical image formed on the liquid crystal panel 45 onto a screen (not shown).
With the above-described configuration, the liquid crystal panel 45 is illuminated with the plurality of lamps 31 and 32, so that it is possible to configure a projection display device with a bright light source for illumination.    [Patent Document 1] JP2000-003612A